The invention relates to apparatus for use in a developer station where charge images formed on a charge image carrier passed through the developer station are inked in accordance with magnetic brush principles with a developer mix of toner and carrier particles and, more particularly, to means for adjusting the level of developer mix being carried on a developer drum to the inking area.
Typically, non-mechanical printing or copying machines function according to electrophotographic or xerographic principles, wherein electrostatic latent images of characters to be printed are generated on a charge image carrier, such as a photoconductive drum, and subsequently inked with a black powder called toner in a developer station. The toner images are subsequently transferred to sheet paper on which they are fixed. The developing station typically includes at least one developer unit generally referred to in the art as a magnetic brush developer. The magnetic brush developer, as a rule, contains a magnetic drum mounted for rotation so as to continually bring developer mix, consisting of iron carrier particles and toner particles, into contact with the electrostatic images recorded on the charge image carrier. The charge images are inked by adherence of toner particles to the charge images due to electrostatic forces. The magnetic drum conventionally comprises a rotating hollow cylinder with a stationary magnet arrangement mounted within. One known developer station assembly which functions in accordance with magnetic brush principles is disclosed in U.S. Pat. No. 3,882,821. A magnetic brush developer station may also include a magnetic roller disposed beneath the developer drum for transporting developer mix particles from the floor of the developer station to the developer roller. This transport roller conventionally comprises a rotating hollow cylinder with a stationary magnet arrangement mounted within.
The developer roller conducts developer mix through an inking gap formed between the developer roller and the moving surface of the charge image carrier for toner inking of the latent charge images. Uniform and efficient inking of the charge images on the charge image carrier requires that the developer mix carried by the developer drum be regulated so as to have a uniform layer thickness and density with the aid of a doctor or stripping device prior to the inking gap. If the layer of developer mix on the developer roller is too thin or of uneven thickness, inking of the charge image carrier may be erratic with pale and spotted character printing. If the layer of developer mix is too thick, the photoconductive surface layer on the charge image carrier may become damaged in the inking gap.
U.S. Pat. No. 3,882,821 discloses the use of a stripping plate adjacent the developer roller for leveling the layer of developer mix being passed to the inking gap, wherein the excess developer mix strip by the plate subsequently falls back into the lower region supply chamber of the developer station. The stripping plates are permanently fixed in the developer housing spaced at a predetermined distance from the developer roller and extending longitudinally therewith. However, a significant disadvantage occurs with the use of such a stripping plate in that toner will from time to time fall from the developer mix layer on the developer roller as a result of its own weight and deposit on the stripping plate. This toner deposit builds up over the course of the operating period and, consequently, is periodically passed back into subsequent developer mix layers passing to the inking gap. This chipping away of the toner deposit on the stripping plate causes uneven inking densities or black spots on the developed charge images and can also cause a blurred printing during development of the carrier images, which is unsuitable and may lead to unintelligible printing.
An object of the present invention is to provide a developer station with apparatus such that developer mix carried on the developer roller is evenly layered prior to passage through the inking gap and periodic build-up of toner deposits adjacent the developer roller are prevented, even in the case of high-speed printers or copiers.